The present invention relates to a photosensitive material and to a process for imaging using the same. More particularly it relates to a photosensitive material in which a plurality of capsules, containing a radiation sensitive composition which undergoes a change in viscosity upon exposure, are distributed upon a support and images are formed by image-wise exposing the capsules to radiation and rupturing the capsules. Exposure renders the internal phase image-wise releasable from the capsules such that by rupturing the capsules and interacting the internal phase with developing agents, images can be formed.
While there are numerous examples of photosenstive materials in the art, none is particularly well adapted for copying documents or copying from microfilm, a reader-printer or a cathode ray tube. Two of the principal disadvantages of silver based imaging systems are their expense and the need for wet development processing. Attempts have been made to reduce the amount of silver used in previous svstems and to develop dry development processings and one outgrowth of these efforts is the thermally developable silver imaging system. For a number of reasons, including a high level of fogging, the image quality of this latter system has not been as high as desired. At the same time socalled silverless systems that have been developed have not provided good sensitivity.
Some imaging systems based on photosensitive encapsulates are known.
Berman, U.S. Pat. No. 3,219,446 discloses a transfer imaging process in which azo-blue-"B" black dye is encapsulated with a photocrosslinkable polymer or a photopolymerizable monomer as a fluid droplet-containing film or a layer of fluid droplet-containing microcapsules. In this system, imaging is accomplished by image-wise exposing a layer of the encapsulate to electromagnetic radiation to cross-link the polymer or polymerize the monomer. This is stated to cause the liquid in the exposed capsules to assume a non-liquid, rigid condition. Images are formed by transferring the dye from the still liquid capsules to a receiving sheet by the use of pressure. Experimentation with the Berman system has shown that it has a very low sensitivity (i.e., requires a comparatively intense exposure to form an image) and provides poor image contrast.
Phillips, U.S. Pat. No. 3,700,439 discloses a photocopy process wherein Michler's ketone is encapsulated in a conventional manner and provided as a layer on a support. Michler's ketone itself is not a color former, but patterned irradiation of the ketone in the capsules converts the ketone to a colorless, acid colorable, dye precursor. When this dye precursor is subsequently contacted with an acid developer, such as acid clay, a visible image is obtained. Phillips discloses both a system in which the exposed imaging sheet is calendered face-to-face with an acid coated receiving sheet to form images and a system wherein the acid developer is on the same surface as the capsule coating so that after rupturing the capsules there is development without transfer.
Neither the Berman nor the Phillips imaging materials is the basis of any commercially available imaging material. In the case of the Berman system, the reason for this is probably the low sensitivity of the material and the poor image quality that is obtained.
Thus, there is a need for a dry-developable, silverless, photosensitive material which can be used for copying from reader-printers, cathode ray tubes and the like which provides good image quality and high sensitivity.